There is conventionally known an electrically-operated type of variable valve timing device which changes a rotational phase of a cam shaft relative to a crank shaft for an internal combustion engine to change opening/closing timing (valve timing) of an intake valve or an exhaust valve. There are proposed a variety of methods for controlling this device (US-2007-0221150A1). In the controller disclosed in US-2007-0221150A1, in a case of changing the valve timing at the stopping of an internal combustion engine, an operational amount of the motor is made smaller than during the operating of the internal combustion engine. In this manner, an operating noise of the variable valve timing device is reduced.
In a case of changing the valve timing after stopping the internal combustion engine, it is required to transfer the cam shaft from a stop state to a rotation state. Specially, for example, in a case where a rotation transmission portion in the variable valve timing device to the cam shaft comprises a plurality of gears, it is required that the gears in the rotation transmission portion are rotated from the stop state by the motor, thereby to change the rotational phase of the cam shaft. There exists an individual difference in dimension between the gears of the rotation transmission portion. Therefore there is a possibility that, caused by a difference in an engaging state of the gears or the like due to the individual difference, the change in the rotational phase of the cam shaft relative to the crank shaft is stopped in the middle of changing the valve timing after the stop of the internal combustion engine. That is, there is a possibility that there occurs a state (lock state) where the cam shaft can not be further rotated.
In a case where this lock state occurs, when the power supply to the motor is continued, there is a possibility that a temperature of the motor or a motor drive circuit for driving the motor rises. In a case where this temperature rise occurs, there is a possibility that the motor or the motor drive circuit is not appropriately operated. As a result, for example, even if power supply control is performed for releasing the lock state at the lock occurrence, the lock state can not be eliminated.